Baths and processes for electrodepositing palladium

ABSTRACT

A process for electrodeposition of palladium is described wherein an electroplating bath comprising a palladium(II) compound is employed which electroplating bath is ammonia-free. The bath contains water and an amine of the formula ##STR1## wherein x=0 or 1 and when x=0: ##STR2## and when x-1: R 1  =N(CH 3 ) (CH 2 ).sub. 3 NH 2 , NH(CH 2 ).sub. 2 NH 2 ,  NH(CH 2 ).sub. 2 NH(CH 2 ).sub. 3 NH 2 ,  NH 2 , OH or C 1-4  -alkoxy,  R 2 , R 3 , R 4  =H or CH 3 . 
     The amine permits the electrodeposition of palladium at a current density above 2.5 A/dm 2  and the resultant coatings are semi-glossy to glossy and are characterized by firm adhesion and freedom of pores. The coatings have only low internal tensions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the use of an amine together with a palladium(II) compound for an ammonia-free, aqueous bath for electrodepositing palladium coats.

2. Discussion of Prior Art

German Patent 23 60 834 describes a bath for electrodepositing palladium coatings which bath contains palladium as complex with an amine of the general formula

    NH.sub.2 --(CH.sub.2 CH.sub.2 NH).sub.n --CH.sub.2 CH.sub.2 NH.sub.2 with n≧3.

From this bath, at current densities between 0.1 and 2.5 A/dm², glossy, palladium coatings, free of cracks and pores, can be deposited. During galvanizing, the pH of the bath remains constant, and in contrast to the slightly ammoniacal baths containing palladium as amine complexes no harmful vapors result.

German Offenlegungsschrift 26 57 925 likewise describes an ammonia-free, aqueous bath for electrodepositing palladium. The bath contains palladium as diglycin palladium(II) complex and aminoacetic acid as complex former.

SUMMARY OF THE INVENTION

It is an object of this invention to provide amines for use together with palladium(II) compounds for ammonia-free, aqueous baths which can be operated also at current densities above 2.5 A/dm² and give firmly adhering, pore-free and tension-free palladium coatings. It is also an object of this invention to provide a process for electrodepositing palladium from these baths.

These objects are achieved according to the invention, by using an amine of the general formula ##STR3## wherein x=0 or 1 and when x=0: ##STR4## and when x=1:

R¹ =N(CH₃)(CH₂)₃ NH₂, NH(CH₂)₂ NH₂, NH(CH₂)₂ NH(CH₂)₃ NH₂, NH₂, OH or C₁₋₄ -alkoxy,

R², R³, R⁴ =H or CH₃ together with a palladium(II) compound for an ammonia-free, aqueous bath for electrodepositing palladium as a coating at a pH of 6 to 11, a temperature of 20° to 70° C. and a current density of 0.1 to 30 A/dm².

Besides 1-(2-aminoethyl)piperidine and 4-(2-aminoethyl)morpholine, there are used as amines in particular N,N,2,2-tetramethyl-1,3-diaminopropane, 2,2-dimethyl-1,3-diaminepropane, N,N-dimethyl-1,3-diaminopropane, N-(2-aminoethyl)-1,3-diaminopropane, N-methyl-bis-(3-aminopropyl)-amine, N,N'-Bis-(3-aminopropyl)-1,2-diaminoethane, N,N,2,2-tetramethyl-3-aminopropanol, 2,2-dimethyl-3-aminopropanol, 3-methoxy-propylamine and 3-butoxypropylamine.

Preferred palladium(II) compounds are PdCl₂, Pd(OH)₂, K₂ [Pd(NO₂)]₄, Pd(NH₂ SO₃)₂, Pd(NH₃)₂ CL₂ and Pd(NH₃)₂ (NO₂)₂.

Preferably, the palladium concentration is 6-20 g/l and the amine is used in an amount which corresponds to a molar ratio of amine to palladium of 1 to 1 to 3 to 1.

Besides amines and palladium(II) compounds, the usual and known per se additions such as conducting salts, buffer salts, wetting agents and brighteners are used.

The surprising advantage of the amines used according to the invention lies in the possibility of being able to operate the so-obtained ammonia-free, aqueous baths also at high current densities. Thus, the baths can be used also with processes that require a high rate of deposition, e.g. in tape galvanizing and in selective galvanizing.

They furnish semiglossy to glossy palladium coatings that are of firm adhesion and free of pores and have only low internal tensions.

The coatings are suitable for industrial purposes, electrical contacts for example, as well as for decorative purposes, jewelry for example.

In the examples that follow, the preparation of baths using the said amines is described and the conditions for electrodeposition of palladium coatings from these baths are given.

Adjustment of the pH of the baths is made with a suitable basic compound, preferably with the amine used, or with an acid, preferably with one whose anions are already present in the bath. pH adjustment can be effected by the addition of a base such as K₃ PO₄ or KOH.

Alternatively, if necessary, an acid such as HCl, HNO₃, H₃ PO₄ or NH₂ SO₃ H can be employed. Salts can be included in the ammonia-free aqueous electroplating bath. These salts include: NaNO₃, K₂ SO₄, KCl, KH₂ PO₄, potassium citrate, Na₂ SO₄ or K₂ HPO₄. Some of these salts can be employed for pH adjustment.

The examples which follow will serve to illustrate the invention without, however, limit it.

EXAMPLE 1

To the solution obtained from an aqueous solution containing 10 g/l Pd as K₂ [Pd(NO₂)₄)] and 60 ml/l N-(2-aminoethyl)-1,3-diaminopropane, 30 g/l NaNO₃ and 5 g/l potassium citrate are added.

At a pH of 8.9, 60° C. and 20 A/dm², firmly adhering, glossy, finger-insensitive palladium coats are deposited.

EXAMPLE 2

To the solution obtained from Pd(NH₃)₂ Cl₂ in an amount corresponding to 10g/l Pd, 20 ml/l N,N'-bis-(3-aminopropyl)-1,2-diaminoethane and water, 20 g/l NH₂ SO₃ H and 20 g/l Na₂ SO₄ are added.

At a pH of 7, 50° C. and 5 A/dm², firmly adhering, semiglossy palladium coatings are deposited.

EXAMPLE 3

To the solution obtained from an aqueous solution containing 10 g/l Pd as Pd(NH₂ SO₃)₂ and 30ml/l N,N,2,2-tetramethyl-1,3-diaminopropane, 25 g/l NH₂ SO₃ H are added.

At a pH of 8.1, 50° C. and 5 A/dm², firmly adhering palladium coatings are deposited.

EXAMPLE 4

To a solution obtained from Pd(OH)₂ in an amount corresponding to 10 g/l Pd, 10 ml/l 2,2-dimethyl-1,3-diaminopropane and water, 10 g/l KH₂ PO₄ are added.

At a pH of 7.5 60° C. and 5 A/dm², firmly adhering, semiglossy palladium coatings are obtained.

EXAMPLE 5

To a solution obtained from an aqueous solution containing 10 g/l Pd as Pd(NH₂ SO₃)₂ and 60 ml/l 2,2-dimethyl-3-aminopropanol, 35 g/l Na₂ SO₄ are added.

At a pH of 8.1, 50° C. and 5 A/dm², firmly adhering palladium coatings are deposited.

EXAMPLE 6

To a solution obtained from an aqueous solution containing 10 g/l Pd as K₂ [Pd(NO₂)₄ ] and 25 ml/l N-methyl-bis-(3-aminopropyl)-amine, 30 g/l K₂ HPO₄ are added.

At a pH of 7.2, 60° C. and 10 A/dm², well adhering, glossy palladium coatings are deposited.

EXAMPLE 7

To the solution obtained from an aqueous solution containing 10 g/l Pd as Pd(NH₂ SO₃)₂ and 40 ml/l 3-methoxypropylamine, 75 g/l K₂ SO₄ are added.

At a pH of 7, 50° C. and 5 A/dm², well adhering palladium coatings are deposited.

EXAMPLE 8

To a solution obtained from Pd(NH₃)₂ Cl₂ in an amount corresponding to 10 g/l Pd, 30 ml/l 4-(2-aminoethyl)-morpholine and water, 30 g/l KCl are added.

At a pH of 8.2, 50° C. and 5 A/dm², semiglossy palladium coats are deposited.

EXAMPLE 9

To the solution obtained from Pd(NH₃)₂ Cl₂ in an amount corresponding to 10 g/l Pd, 25 ml/l 1-(2-aminoethyl)-piperidine and water, 40 g/l KCl are added.

At a pH of 7.8, 50° C. and 5 A/dm², semiglossy palladium coatings are deposited. 

What is claimed is:
 1. In a process of electrodepositing a palladium coating on a substrate employing a palladium (II) compound in an amine-containing ammonia-free aqueous electroplating bath, the improvement wherein said amine is one of the formula

    R.sup.1 --CH.sub.2 --CH.sub.2 --NH.sub.2

wherein ##STR5##
 2. A process according to claim 1, wherein the electrodeposition is effected at a pH of 6 to 11, a temperature of 20° to 70° C., and at a current density of 0.1 to 30 A/dm².
 3. A process according to claim 1, wherein the electrodeposition is effected at a current density of above 2.5 A/dm².
 4. In a process of electrodepositing a palladium coating on a substrate employing a palladium (II) compound in an amine-containing ammonia-free aqueous electroplating bath, the improvement wherein said amine is selected from the group consisting of: N,N,2,2-tetramethyl-1,3-diaminopropane, 2,2-dimethyl-1,3-diaminopropane, N,N-dimethyl-1,3-diaminopropane, N-(2-aminoethyl)-1,3-diaminopropane, N-methyl-bis-(3-aminopropyl)-amine, N,N'-bis-(3-aminopropyl)1,2-diaminoethane, N,N,2,2-tetramethyl-3-aminopropanol, 2,2-dimethyl-3-aminopropanol, 3-methoxypropylamine and 3-butoxypropylamine.
 5. An ammonia-free aqueous bath for electrodepositing palladium containing a palladium (II) compound and an amine of the formula:

    R.sup.1 --CH.sub.2 --CH.sub.2 --NH.sub.2

wherein ##STR6##
 6. An ammonia-free aqueous bath for electrodepositing palladium containing a palladium (II) compound and an amine selected from the group consisting of: N,N,2,2-tetramethyl-1,3-diaminopropane, 2,2-dimethyl-1,3-diaminopropane, N,N-dimethyl-1,3-diaminopropane, N-(2-aminoethyl)-1,3-diaminopropane, N-methyl-bis-(3-aminopropyl)-amine, N,N'-bis-(3-aminopropyl) 1,2-diaminoethane, N,N,2,2-tetramethyl-3-aminopropanol, 2,2-dimethyl-3-aminopropanol, 3-methoxypropylamine and 3-butoxypropylamine. 